Blasting cap manufacture



July 18, 1950 V E. K. LEFREN 2,515,238

BLASTING CAP MANUFACTURE Filed May 1a, 1946 FIG.6 F1012 EDWARD K4 LE FREN INVENTOR.

BY Mg. PM

AGENT Patented July 1 2,515,238 nLAs'rrNo c urllo'rn Edward K. Lefren, Kingston, N. Y., asslgnor to Hercules Powder Company, Wilmington, DeL, a. corporation of Delaware Application May 18, 19%, Serial No. 670,795

Claims.

Thisinvention relates to electric blasting initiators and more particularly to a novel and improved method for the manufacture of Waterproof electric blasting initiators.

According to one method of manufacturing electric blasting initiators, the leg wires are cur-- bedded in a hard cast plug of sulfur which is then inserted into the open end or a charged shell and sealed by a heated mixture poured in behind it. Such a method is subject to several disadvantages. Considerable handling is required which is always disadvantageous in view of the sensitive nature of the explosives employed. Also, unless consid erable care and skill are exercised when intro clucing the waterproofing compound, it is quite likely that some of it will enter the explosive charge with deleterious eilects. Moreover, a relativel large amount of the sealing compound is required to protect the cap against moisture when stored under adverse conditions. Thus, a longer initiator shell is required. Furthermore, this method is complicated, time consuming and expensive and does not always give a closure which will retain its waterproofness under adverse conditlons.

Another method, of more recent origin, comprises molding and compressing a heated material about the leg wires of the electric blasting initiator to form a plug, inserting the plug in the shell and crimping the shell into the plug to form the seal. This method has many advantages but is subject to the disadvantage that the operation of molding the material around the leg wires is complicated, costly and time consuming and is likely to result in an inferior product. In this operation, the temperatures utilized are sufiiciently great to cause softening of the insulation material of the wires and a consequent intermingling of this material with the thermoplastic plug material. The result is undesirable from the standpoint of effective molding and adversely afiects the strength, durability and appearance Of the product. There is moreover a tendency to weaken the insulation adjacent to but exterior of the plug with the result that it soon cracks and exposes the bare wires, thus increasing the possibility of short circuits and other failures. Attempts to overcome this result in further complication and increased cost of the process.

Additionally, in this type of operation, it is necessary to handle relatively long lengths of leg wire and to maintain the ends thereof in fixed positions during the molding operation. This is diflicult and exacting and represents another disadvantage inherent in such procedure.

tion to construct the ignition plug assembly with out softening or otherwise adversely affecting the leg wires or the insulation thereon. Another object of the invention is to providean ignition plug which may be assembled in waterproof relation with the initiator shell without the use of interior sealing compounds. These and other objects will be apparent as the description proceeds.

It has been found that the foregoing objects are accomplished and the disadvantages overcome by the method of this invention which comprises forming a plug of dielectric material without leg wires, extending a pair of pins through the plug, attaching a pair of leg wires to one end of the pins, advancing the pins to move the connections thus formed within the plug, afixing a bridge wire to the other end of the pins, and inserting the completed ignition plug into an initiator shell.

In accordance with this invention, the plug is desirably molded by heat and pressure into the desired shape and size. Openings, extending through the plug, are provided adjacent one end thereof in communication with a recess provided at the opposite end. The pins are inserted through the openings and the recess so that the ends of the pins protrude from the end of the plug. Leg wires are then soldered, welded or otherwise attached to the pins, an insulating and sealing compound introduced into the recess, and the pins pulled partly through the plug to move the bare ends of the wires into the insulating and sealing compound contained -in the recess. The sealing compound is then hardened to produce a rigid, watertight connection. The pins are anchored against a pulling force on the leg wires by ears or nicks made in the pins adjacent the plug. The pins are then cut off a predetermined distance from the end of the plug and the bridge wire afiixed by soldering or welding. The completed ignition plug is then assembled with the initiator shell in watertight relationship.

Having now described the invention in general terms, there follows a more detailed description of preferred embodiments thereof with reference .to the accompanying drawings in which: Fig. l is a transverse cross-sectional view of the plug; Fig.

' 2 is a transverse cross-sectional view ofthe plug showing the pins in place; Fig. 3 is a transverse cross-sectional view of the plug showing the pins in place and the leg wires attached thereto; Fig. 4 is a view similar to Fig. 3 showing the sealing compound in the recess; ig. 5 is a view similar to Fig. 4 showing the pins and wires moved to embed the bare ends of the leg wires in'the sealing material; Fig. 6 is a view similar to Fig. 5 showing the pins after they have been eared or nicked; Fig. 'l is a similar view showing the pins after they have been cut off; Fig. 8 shows the addition of the bridge wire to form the completed ignition plug assembly; Fig. 9 is a transverse cross-sectional view of the assembled initiator; Fig. 10 is a view similar to Fig. 9 but shows the end of the shell clamped down over the end of the plug; Fig. 11 is a transverse sectional view of a modified plug with the pins in position; and Fig.

12 is a transverse cross-sectional view of a modifled type of initiator.

Referring now to the drawings, Figs. 1 through 10 illustrate the various stages of construction involved in the manufacture-of a blasting initiator according to a preferred embodiment of this inopen ngs l2 and I3, and the recess II. The pins may be suitably tapered to permit easy entry and passage through the plug.

Fig. 3 shows the plug and pin assembly with the leg wires l8 and I soldered or welded to the ends of the pins. Beads 20 and 2| are formed at the pin and wire Joint as a result of the soldering or welding operation.

Figs. 4 and illustrate the addition of the sealing compound 22 (Fig. 4) and the embedding of the bare ends of the leg wires therein (Fig. 5). The latter operation is accomplishedby pulling the pins l8 and I! through the plug in the direction of the arrow shown in Fig. 5. This draws the bare ends of the leg wires into the soft insulating and sealing compound 22 which is subsequently hardened to form a rigid waterproof connection between the wires and plug.

Fig. 6 illustrates the step of earing or nicking the pins It and I1 as shown by the ears 23 and 24, respectively, and Fig. 7 illustrates the step of cutting oil. the pins i 6 and i I at a predetermined distance from the end of the plug after caring.

Fig. 8 illustrates the step of attaching the bridge wire 25 to the pins l8 and I1.

Fig. 9 shows the initiator shell I6 and ignition plug Iii assembled in watertight relationship. Ordinarily a waterproof joint is obtained by making the outside diameter of the plug slightly larger than the inside diameter of the shell and pressing the plug into the shell. This causes the latter to expand or bulge as at 20 and to frictionally hold the plug in a tight grip. Insertion may be facilitated by slightly tapering the entrance end of the plug, as at ll, or by'slightly flaring the open end of the shell.

Fig. shows the completed initiator with the end of the shell folded around the end of the plug I as at 29 to act as an additional means for holding the assembly in tight relationship.

The completed initiator resembles the normal device of thistype except that it is considerably shorter andhas' the slight bulge heretofore men- 1 tioned which is hardly perceptible to the naked eye. The bulge will not normally increase the shell diameter more than about 0.003 inch but may be as much as 0.04 inch depending on the shell characteristics and the plug diameter.

is The plugs, in accordance with the preferred form of this invention, are formed from a hard dielectric material such as the thermosetting or thermoplastic resins. The material selected should be of suillcient hardness to expand the shell and produce the bulge heretofore mentioned as well as highly resistant to cold flow.

The plugs will normally be cylindrical in shape, ;with a diameter from about 0.003 inch to about 0.005 inch greater than the inside diameter of the shell, and a length fromabout 54 inch to about inch.

The openings l2 and ii are designed to facilitate entry and to insure correct spacing and alignment of the pins l6 and I1. They may be so the same size as the pins but are preferably slightly smaller to insure a snug fit. They may extend completely through the plug or only partially therethrough. Depending upon the specific design of the mold, there may be a thin film 'of the plug material over one end of the openings. However, the pins are readily pushed through this film.

The recess II is designed to receive the bare ends of the leg wires and to provide space for the 40 introduction of a suitable amount of insulating and sealing compound. It should therefore have a a suitable cross-sectional shape and depth to accomplish these purposes. It has been found preferable to employ a recess in which the cross-sectional shape is rectangular with rounded corners and the depth in the order of about V4 inch for a plug having a length of about 1; inch. However, other cross-sectional shapes and other depths may be utilized with satisfactory results. In

some cases, it may be desirable to provide separate recesses foreach wire as shown at 32 and 33 in Fig. 11. In other cases, the recess may be omitted with, however,- probable adverse effect on the tightness, rigidity and waterproofness of the assembly when using a hard dielectric material for the plug. All such modifications and alternative forms of construction are within the purview of this invention.

Plug materials suitable for use in the preferred form of this invention are required to have a compressive strength greater than the tensile strength of the shell. Plastic materials having a compressive strength above about 6,000 lbs./sq. inch, preferably between 16,000 and 40,000

lbs/sq. inch, a compression modulus of elasticity above 1.3 10 lbs/sq. inch, preferably between x10 lbs/sq. inch and 50x10 lbs/sq. inch, and coefficients of thermal expansion between about 2 .10 and 16 10- inches per inch per 7 degree centigrade are preferred. Thermosetting resins, such as alkyd resins, phenol-formaldehyde resins, cresol-aldehyde resins, xylenol -aldehyde resins, urea-formaldehyde resins, phenol-furfural resins, thiourea-forma-ldehyde resins and sulfonamide resins, are satisfactory. Thermoplascordance with a modified form of the invention,

other materials may be used for the plug as will 'be pointed out hereinafter.

The pins l6 and I! must be sufficiently stiff to permit passage through the plug without bending or breaking and also to resist bending or displacement in the subsequent operation of assembling the plug and shell. Suitable materials for this purpose are iron, steel, copper, nickel, nickel silver, silver and Invar. The diameter of the pins is .preferably about 0.0005 inch larger than the inside diameter of the holes in the plugs, but may vary under some circumstances to a point wherein the hole in the plug is about 0.0002 inch larger than the wire diameter. It is preferred to use a wire diameter of 0.035 inch and a plug hole diameter of 0.0345 inch. The length of the pins is determined by the length of the plug and is usually from about A; inch to about inch longer than the plug. The pins may be inserted in and through the plugs by hand or by mechanical means.

The leg wires which are used in the method of this invention are the normal wires used in the art. Thus, they may be copper wire, or iron wire, either plain or tinned. They may be insulated in a desirable manner such as, for example, by using enamel, cotton servings, or plastic materials.

The leg wires are secured to the pins preferably by welding. This insures maximum strength and conductivity. Desirably a head is formed at the welded joint to increase its efiectiveness. Although welding is preferred, other securing means, such as soldering, may be used.

In thgpreferred embodiment, the insulating and sealing compound 22 effectively insulates the bare end portions of the leg wires and forms a strong waterproof assembly of the pins and leg wires with the plug. Preferred materials for sealing should be hard and durable under all normal temperature conditions and capable of being rendered soft or semifiuid for the initial application. Where a molten sealing compound is used, the temperature will in all cases be insufflcient to adversely afiect the wire insulation thereon. The insulating and sealing compound, preferably a material which hardens by the addition of a setting-up agent or quick evaporation of solvents, may be introduced in any suitable manner either mechanically or by hand. Suitable materials for this purpose are waxes, asphaltic materials, thermoplastic compounds or combinationsof these. Other materials of a like nature may be used without departing from the scope of the invention.

The bare ends of the leg wires are pulled into the sealing compound while it is still molten and/or soft. This is accomplished by sliding the pins l6 and I! through the plug ID in the direction of the arrow shown in Fig. 5. This may be done manually or by suitable mechanical devices.

The ears 23 and 26 are made by slightly deforming the pins l6 and 11 adjacent the plug. Care must be exercised to see that the pins are not substantially weakened thereby. The ears increase the pull-out resistance of the leg wires from the plug.

The bridge wire 25 used to connect the ends of the pins l6 and I! may be electrically resistant wire composed of noble or base metal, or alloys thereof. Thus, for example, platinum, Nichrome,

copper-nickel, or other alloys may be employed.

The bridge wire is welded, soldered or otherwise secured adjacent the ends of the pins after they have been cut oil a predetermined distance from the face of the plug.

In assembling the shell and plug, it has been found that the diameterof the plug and the shell provides the control for the waterproof seals. Best results are obtained when the plug has a diameter between about 0.003 inch and about 0.005 inch greater than the. inside diameter of the shell. Insertion is accomplished by means of a press.

In some cases, additional assurance of a waterproof seal, under extreme conditions, is obtained when a waxymaterial is utilized. The waxy material may be applied to the surface of the plu or to the shell in the vicinit of the plug, or may be incorporated in the plug, or may be utilized in any combination of these. When the wax is incorporated in the plug material prior to molding an amount less than 5% by weight of the material, and preferably between about to about 3% is used. A combination of admixture and suitable include palm, ceresin, montan, stearin,-

beeswax, spermaceti, synthetic waxes and similar materials. In addition to contributing assurance of waterproofness, the presence of a wax also reduces the force required to insert the plug in the shell. I

The initiator shells used in the preferred embodiment of this invention are the normal type commonly used. They may be prepared of any desirable copper alloy, aluminum, bronze or similar ductile metallic materials. The strength and thickness of the walls should be such that splitting does not occur when the oversized plug is forced thereinto. If desired, the upper portion of the shell may be constricted slightly before insertion of the plug and thus produce a shell with straight sides. 'However, production of the enlarged or expanded upper base portion type shell is preferred because of the ease of manufacture.

The explosive charge 22 is shown to consist of a single charge of material, but this explosive charge may be any of the normal explosive charges used in blasting caps. Thus, for example, it may consist of an admixture of mercury fulminate and potassium chlorate, or it may consist of a base charge of tetryl, nitrostarch, pentaerythritol tetranitrate, and the like, having superimposed thereon a charge consisting of an admixture of mercury fulminate and potassium chlorate, diazodinitrophenol and potassium chlorate, or lead azide and the like, The use of'the various known explosive compositions and' their arrangement within the cap are well known to the art and do not form part of the present invention.

In accordance with the preferred embodiment of this invention, the plugs may be formed by compression, transfer or injection molding methods. The compression and transfer methods of molding are preferred for the hard thermosetting resins; the injection molding method is preferred for the thermoplastics. These molding methods are likewise preferred when using resilient material wherein it is desired to provide the recess in the plug.

When utilizing resilient material such as rubinto units to form the individual plugs. The pins are inserted into the apertures of the individual plug units and the leg wires are aflixed to the pins. The connecting joint between the leg wires and pins is then pulledinto the apertures of the resilient material. With this method, the recess is not necessary. Alternatively, the resilient material may be extruded with two wires embedded therein and extending the length of the extruded strand. The strand is then cut into units to form individual plugs. The wires embedded therein serve as the pins. The plug is then compressed to expose the ends of the pins for aiiixing the leg wires thereto. The connection joint is then pulled or pushed into the resilient material thereby exposing the other end of the pins. The bridge wire is then aflixed to the exposed end of the pins. With this method, the recess is likewise unnecessary. It is common practice'to crimp the initiator shell into resilient plugs of this type. Thus the compression of the resilient material servesto insure a tight and waterproof ignition assembly.

The embodiment utilizing resilient material is shown in Fig. 12 wherein the plug 34 is securely held by the crimps 38 and 31 in the shell 35, thus forming a watertight connection. In accordance with this embodiment, it is desirable to utilize materials of a vulcanizable resilient nature such as crude rubber, rubber substitutes, etc.

The method of this invention is equally appli- 1 cable to the manufacture of other ignition assemblies such as the matchhead type.

The foregoing method of manufacture, as well as the electric blasting initiator resulting therefrom, offers many advantages over the art. By molding the plug in a separate operation, it has :been possible to eliminate the disadvantages inherent in the old procedure of molding the plug around the leg wires. Thus, in accordance with this invention, it is not necessary to handle long lengths of leg'wires and to hold the ends thereof in fixed positions in the mold during the molding operation. Further, there is no danger of damaging the insulation on the leg wires nor of causing the intermingiing oi the insulation material with the plug material.

The utilization of pins, in the manner set forth, results in a procedure which is faster, less com- .plicated and easier to mechanize than heretofore known. It is, therefore, possible to eflect greater economy and production when following the teachings of this invention.

A further advantage resides in the elimination of the hazardou operation of pouring a molten sealing compound into a shell loaded'with explosive. As a result, less handling and manipulating of a sensitive explosive are required.

The electric initiator manufactured in accordance with this invention has greater strength and water-resistant properties, is shorter and less expensive than the ordinary type of device used for What I claim and desire to protect by Letters Patent is:

1. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a pair of openings extending substantially therethrough, inserting a pair of pins into the openings so that the ends of the pin protrude from at least one end a of said plug, securing the bare ends of a pair ofend opposite the leg wires.

2. In the method of producing an electric blastleg wires to the adjacentprotruding ends of the pins, moving the pins relative to the plug to em-. bed the bare portions of the securing a,=bridge'wire to the pins adjacent the ing initiator the improvement comprising forming a plug of dielectric material having a pair or openings extending substantially therethrough; inserting a pair of pins into the openings so that the ends of the pin protrude from at least one end of said plug, securing the bare ends of a pair of leg wires to the the pins, moving the pins relative to the plush embed the bare portions of the wires in the plug, earing the pins adjacent the plug to prevent sub-- sequent pulling out, and securing a bridge wire toirthe pins adjacent the end opposite the leg w es. 3. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a pair of openings extending substantially therethrough,

end of said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug, earing the pins adjacent the plug to prevent subsequent pulling out, cutting of! the ends of the pin at a predetermined distance from the plug, and securing a bridge wire to the pins adjacent the end opposite the leg wires. 4. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a recess adjacent one end and a pair of spaced openings adjacent the opposite end and extending into said recess, inserting a pair of pins into the openings so that the ends of the pins extend into the recess, securing the bare ends of a pair of leg wires to the ends of the pins extending into the recess. filling the recess with a sealing material adapted to form a liquid-tight joint between the wires and the plug, moving the pins relative to the plug to embed thebare ends of the wire in the sealing material, and securing a bridge wire to the pins adjacent the end opposite the, leg wires.

5. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a recess adjacent .one end and a pair of spaced the recess, filling the recess with a sealing ma terial adapted to form a liquid-tight point between the wires and the plug, moving the pins relative to the plug to embed the bare ends of the wire in the sealing material, caring the pins-adjacent the plug to prevent subsequent pulling out, and securing a bridge wire to the pins adjacent the end opposite the leg wires.

. 6. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a recess adjacent one end and a, pair of spaced openings adjacent the opposite end and extending into said recess, inserting a, pair of pins into the openings so that the ends of the pins extend wires in the plug, and

adjacent protruding endsof into said recess, securin the bare ends of a pair of leg wires to the ends of the pins extending into the recess, filling the cavity with a sealing material adapted to form a liquid-tight joint between the wires and the plug, moving the pins relative to the plug to embed the bare ends of the wire in the sealing material, hardening the sealing material, earing the pins adjacent the plug to prevent subsequent pulling out, cutting on the ends of the pin at a predetermined distance from the plug, and securing a bridge wire to the pins adjacent the end opposite the leg wires.

7. In the method of producing an electric blasting initiator the improvement'comprising forming an elongated plug of dielectric material, cutting the elongated plug into a plurality of shorter plugs of predetermined length, inserting a pair of pins into each of the shorter plugs so that the ends of the pins protrude from at least one end of saidplugs, securing the bare ends of a pair of leg wires to the adjacent protruding ends of each pair of pins, moving the pins relative to the plugs to embed the bare portions of the wires in the plugs, and securing a bridge wire to each pair of pins adjacent the ends opposite the leg wires.

8. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a pair of openings extending substantially therethrough, inserting a pair of pins into the openings so that the ends of the pins protrude from at least one end of said plug, securing the bare ends of a pair of leg wires to the adjacent protruding ends of the pins, moving the pins relative to the plug to embed the bare portions of the wires in the plug, securing a bridge wire to the pins adjacent the end opposite the leg wires, and inserting the plug assembly in the open end of a blasting initiator in watertight relation therewith.

9. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a recess adjacent one end and a pair of spaced openings adjacent the opposite end and extend- Certificate of Correction i ing into the recess, inserting a pair of pins into the openings so that the ends of the pins protrude from at least one end of said plug, securing the bare ends of a pair of leg wires to the ends of the pins extending into the recess, filling the cavity with a sealing material adapted to form a liquid-tight joint between thewires and the plug, moving the pins relative to the plug to embed the bare ends of the wire in the sealing material, securing a bridge wire to the pins adjacent the end opposite the leg wires, and inserting the plug assembly in the open end of a blasting initiator in watertight relation therewith.

10. In the method of producing an electric blasting initiator the improvement comprising forming a plug of dielectric material having a pair of openings extending substantially there- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATEN'I'S Number Name Date 598,106 Lowe Feb. 1, 1898 991,373 Rennie et al May 2, 1911 1,606,413 Grant Nov. 9, 1926 1,898,011 Hammond Feb. 21, 1933' 1,933,694 Allen et al. Nov. 7, 1933 2,105,674 Sosson Jan. 18, 1938 2,139,581 Hanley Dec. 6, 1938 2,150,374 Johnson et al Mar. 14, 1939 2,215,066 Clark Sept. 17, 1940 2,228,878 Johnson et al. Jan. 14, 1941 2,240,438 Durant Apr. 29, 1941 2,382,921 Seavey 'Aug. 14, 1945 2,399,034 Huyett et al. Apr. 23, 1946 July 18, 1950 EDWARD K. LEFREN It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction joint and that the said Letters Patent should be read as follows: Column 8, lines 1 and 13, for the word pin read pins; line 62, for point read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of October, A. D. 1950.

"THOMAS F. MURPHY,

, Assistant Oommisszoner of Patents. 

